In the manufacturing of pneumatic tires certain of the components thereof are formed of elastomeric materials which are extruded into elongated strips or sheets of the extrudate for subsequent placement on a tire building drum. One type of extrudate produces the innerliner of a pneumatic tire which provides the air impervious component of the tire. It is critical that this innerliner be free of imperfections or perforations which could ultimately leak when the tire is subjected to the high internal pressure since the innerliner provides the air retention layer in a tubeless pneumatic tire.
Heretofore, prior art extrusion apparatus and methods generally used two separate extruders and a roller to combine two or more extrudate streams in forming the final extrudate in order to produce a high integrity innerliner. The combining of two or more streams of extrudate is desirable when forming the innerliner since such a construction very much reduces the chance of a discontinuity of one stream lining up with a discontinuity in the other stream thereby producing a laminate or innerliner of a very high integrity, that is, one having no through apertures in the innerliner or extruded sheet.
Examples of known prior art extrusion heads and methods for forming an extruded product are shown in the following patents.
U.S. Pat. No. 3,941,544 discloses an apparatus for the manufacture of thermoplastic extruded profiles wherein the thermoplastic stream from the extruder is divided into a conical flow channel. A lattice is inserted into the flow channel which partitions the channel into a plurality of individual channels. The thermoplastic stream is then combined in a joining section or die before the combined extrudate exits from a nozzle.
U.S. Pat. No. 3,985,654 discloses a filter assembly for filtering fluid polymeric material in which a filtering element is composed of a sheet of filter material which define the sides of a chamber. The filter element is incorporated as a component part of an extrusion die head for removing foreign materials and has a plurality of annular slots or passages through which the polymeric material flows when moving into the main chamber.
U.S. Pat. No. 4,017,240 discloses an extrusion apparatus for extruding sheets of rubber or plastic. A conventional screw extruder has an adapted nozzle attached at a rear flange thereof. The nozzle has a tapered bore which reduces the cross-section of the elastomer material and divides the flow into a plurality of thinner strands which are eventually combined to form a relatively wide sheet having essentially uniform strength across its width.
U.S. Pat. No. 4,619,802 discloses an extrusion apparatus comprising a die and a stream combining adaptor. A thermoplastic stream flows through a pair of channels and converges at the point of confluence of both channels and a combined flow stream or passage is formed. Laminate product flows through a manifold chamber and exits through another channel. Molten thermoplastic streams enter the pair of flow channels and are spread into other channels or manifolds and converge at confluence points to form a layered melt stream.
U.K. Patent Application No. GB2,131,734 discloses an extrusion head for producing flat profiles from rubber or plastic material wherein replaceable inserts are used to define flow channels. The profile of the extruded material is changed by replacing one or both inserts. This system uses a plurality of extuders to form a profiled laminate.